Monday, November 16, 2015

Did a missing trace element trigger mass extinctions?

[Cosmos Magazine] An asteroid wiped out the dinosaurs and volcanic eruptions triggered “the Great Dying” at the end of the Permian. But the cause of our planet’s other three mass extinctions is a mystery. Could something as prosaic as dietary deficiency be to blame?
Palaeontologist John Long from Adelaide’s Flinders University thinks a selenium shortage crippled life on Earth at the end of the Triassic, Ordovician and Devonian periods. He and his colleagues published their work in Gondwana Research in November.
The study sprang from a hunt for minerals. Geologist Ross Large from the University of Tasmania was relying on the fact that the trace element selenium is often found near nickel and copper ore deposits. Large meticulously analysed trace elements in 4,000 samples of ocean sediments laid down over the past 560 million years.
Having amassed such a vast dataset, Large offered Long a look at it. The palaeontologist immediately noticed something intriguing: selenium levels plummeted just ahead of the three mysterious mass extinctions.
Selenium is an essential element for all forms of cellular life: it helps cells mop up damaging molecules called free radicals. Along with other essential trace elements, selenium enters rivers and seas when the Earth’s tectonic plates are active. As the plates grind into each other, mountain ranges rise. And as the mountains erode, sand and dust rich in trace elements into rivers and oceans, and marine organisms flourish.
But in periods where landmasses are drifting apart – such as 200 million years ago, when the vast supercontinent Pangaea was breaking up – selenium levels can collapse. Read More